Caulking materials, bonding fluids, sealants etc are usually sold in a cartridge, with a movable back plate at one end and an outlet at the other end, for use in a caulking gun. The caulking gun includes a cradle for the cartridge and a piston that acts on the movable end wall of the cartridge. The outlet end of the cartridge is secured on the gun by a plate having an opening. A nozzle is attached to the opening in the cartridge and extends through the opening in the front plate of the caulking gun. As the trigger is pressed the piston of the caulking gun advances and presses the movable wall of the cartridge resulting in extrusion of the contents through the cartridge opening and the nozzle.
A problem occurs when pressure is released by the operator releasing the trigger as fluid residues continue to discharge through the outlet and the nozzle. This creates waste and spillages that have to be cleaned up. This adds to the work time and inconvenience for the workman.
This problem of over ejection or drool has been addressed in U.S. Pat. Nos. 4,009,804, 4,572,409, 5,236,105, 5,529,225 and 6,119,903 all of which modify the trigger and piston operation of the caulking gun to produce a backward movement of the piston to retract the material back from the outlet. In practice these solutions have not proved successful.
It is an object of this invention to overcome this problem in an inexpensive and convenient manner.